1. Field of the Invention
This invention comprises an improved apparatus and method for localizing cancer tumors on or near the tissue surface based on the use of long wavelength visible or near infrared excitation of intravenously injected porphyrins and monitoring the resultant infrared fluorescence.
2. Description of the Contemporary and/or Prior Art
There is a great deal of concern and interest in the medical and scientific community that an improved means to detect cancerous tumors be devised. In order to decrease the death rate due to cancer, early diagnosis, localization, and therapy must be undertaken. Early detection of tumor lesions of only a few millimeters in extent and 100 micrometers thick is possible by sputum cytology and immunodiagnostic procedures. However, such small preinvasive lesions are not localizable by conventional radiography, computer tomography or nuclear medicine techniques.
It is currently known that when certain porphyrin preparations, such as hematoporphyrin (HP) or hematoporphyrin derivative (HPD), are injected intravenously into the human body, they are selectively retained by cancerous tissue. Two or three days after injection, significantly higher levels of hematoporphyrin are retained in cancerous tissue. The selective retention of porphyrins, such as hematoporphyrin, by cancerous tissue has been used clinically as a "tumor-specific marker". It is known in the prior art that in the presence of ultraviolet or short wavelength visible light, the "tumor-specific marker" absorbed by the cancerous tissue will exhibit a bright red light fluorescence while normal tissue appears light pink.
A discussion of clinical investigations using the visible fluorescence of a "tumor-specific marker" to localize malignant tissue can be found in an article entitled "Hematoporphyrin Diacetate: A Probe to Distinguish Malignant from Normal Tissue by Selective Fluorescence" by R. W. Henderson, G. S. Christie, P. S. Clezy and J. Lineham, British Journal of Experimental Pathology, Volume 61, pp. 325-350 (1980). Another reference by D. R. Doiron and A. E. Profio entitled "Laser Fluorescence Bronchoscopy for Early Lung Cancer Localization" published in "Lasers in Photomedicine and Photobiology" (1980) teaches the use of a laser fluorescence bronchoscope to detect and localize small lung tumors by observing this red fluorescence.
Such prior art techniques have been used to develop endoscopes which use, in addition to the normal viewing white light, a supplementary violet light (at approximately 4200 .ANG.). The violet light is used to excite hematoporphyrin or hematoporphyrin derivative, the tumor-specific markers which are dissolved in an appropriate buffer solution and intraveneously injected into the patient. The porphyrin tumor-specific marker is selectively retained by cancerous tissue and when exposed to the violet light emits a relatively bright red light fluorescence (at approximately 6,000-7000 .ANG.), whereas the surrounding tissue emits only weakly. Similar techniques have been used to localize malignant tissue in the spleen, liver, bladder, kidney, and lungs.
The prior art techniques have one major limitation--only tumors on or near the tissue surface may be detected due to the high transmission loss of the short wavelength violet excitation light. This transmission loss is due to both absorption and scattering of the light by the patient's tissue and/or skin. Tumor lesions occluded by healthy tissue are not detectable using the prior art techniques.